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they done well at not getting locked into MS technology.
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And they chose to go with Fox.....

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And I thought there are tons a VFP developers looking for work, why are they locked into me?
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I put the call out for an awesome opportunity in Philly and got 1 bite. My guess is that a lot of Fox developers have moved on.

Tell me...did you give the client the source code????

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Is there a particular issue that will cause the "likely scaleability" problems with VFP/DB2 I should be aware of?
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The likely scalebility issues you have arise from a tight integration between the UI and the business rules. Just a guess. Also, if they want to go to a web-based UI to expand reach and flexibility, likely, your Fox solution will not provide a lot of help.